Expression of CTLA-4 (CD152) on human medullary CD4⁺ thymocytes

Abstract

CTLA-4 (CD152) is a T cell surface receptor with sequence homology to the co-stimulatory molecule CD28. The molecule, which is essential for the inhibitory regulation of the immune response, becomes transiently expressed on mature T cells after stimulation in vitro. In situ, CTLA-4⁺ T cells are enriched in the light zones of the germinal centers in human peripheral lymphoid organs. In this study we have studied expression of CTLA-4 in human thymus in situ. CTLA-4 was expressed on about one third of CD4⁺/CD8^–/CD1^– medullary thymocytes. CTLA-4 was acquired by a subset of immature (CD1⁺) thymocytes and lost from the mature (CD1^–) subpopulation within 48 h of cell culture, suggesting that the expression on medullary thymocytes is transient. The demonstration of CTLA-4 on a substantial subpopulation of mature CD4⁺ thymocytes adds a new dimension to the understanding of this important molecule. When contemplating application of anti-CTLA-4 for therapy its potential influence on T cell maturation has to be taken into account.